Vehicles with ground-engaging endless track chain assemblies have been recognized for their ability to traverse over rough and muddy terrain while exhibiting a high drawbar pull-to-weight ratio. Accordingly, the track chain assemblies, and particularly the individual track shoes thereof, have experienced considerable research development. The standard track shoe consists of a steel plate with a single grouser or cleat running across its width. While this generally affords good traction, such single grouser track shoes will not grip on frozen ground and they tend to damage the surfaces over which they travel. They also suffer the disadvantage of shoe instability or rocking.
Alternately, two or three grouser track shoes are used because they do not dig up the ground in spinning or turning as much as a single grouser, and they retain more traction than a substantially flat track shoe. Other considerations, such as strength and wear characteristics, and the ability of the shoes to maintain traction although being exposed to clogging mud and icing conditions, are also of paramount importance.
The specific construction of track shoes is also complicated when they are removably secured to a cylindrical mounting belt which is disposed about the periphery of a rubber tire. Such flexible track belt assemblies are used on rubber tired vehicles in order to increase traction, improve flotation and protect the pneumatic carcass from penetration by foreign objects. Reference is made to the flexible track belt assemblies disclosed in U.S. Pat. No. 3,601,212, issued Aug. 24, 1971 to R. A. Peterson et al; U.S. Pat. No. 3,773,394 issued Nov. 20, 1973 to C. E. Grawey and U.S. Pat. No. 3,776,291 issued Dec. 4, 1973 to R. L. Boggs and which are assigned to the assignee of the present invention. In general, the track belt assemblies of the aforementioned patents utlize a plurality of closely coupled track shoes with multiple grousers, because single grouser shoes suffer from the various deficiencies enumerated above.
Double grouser track shoes are particularly desirable in the environment of a flexible track belt assembly and rubber tire. One reason is that the double grouser shoes generally exhibit a heavier longitudinal cross section, including a higher grouser, and this provides additional service wear life. This is particularly beneficial when the vehicle is operated in rock. Another feature is that such shoes may more conveniently be secured to the mounting belts by incorporating suitable fastening devices in the recesses between the two grousers. A further advantage involves improved vibration control through decreased chordal action of the relatively short length shoes and double grousers.
Unfortunately, as a result of mud packing between the grousers, the double grouser track shoes experience a decrease in traction and consequently a tendency of the flexible track belt assemblies to slip in the normal driving direction, as well as a tendency of the vehicle to slip sideways when it is being operated on side slopes. Such adverse operating conditions are naturally aggravated by the usual freezing and thawing conditions accompanying seasonal changes.
For reasons of manufacturing economy, double grouser shoes are preferably rollably formed from hot steel in the direction of the grousers. Therefore, these shoes have a substantially uniform cross section transverse thereto. This manufacturing method substantially eliminates the adoption of complex grouser designs, such as those having diagonal or chevron grouser shapes which could improve the side hill stability of the shoes.
Many of the prior art track shoes are simply not adaptable to various dry and muddy ground conditions or are simple enough in construction to be economical. Frequently, they have various dead-end openings and crevices in which mud and the like can compact, and this markedly reduces the effective tractive effort thereof. Representative of such shoes is U.S. Pat. No. 2,389,156 issued Nov. 20, 1945 to H. A. Knox. Besides having the aforementioned disadvantages, the laterally spaced cleats of the reference patent extend outwardly cantileverably beyond the side edges of the shoe, thus decreasing the flotation capability for a give overall width. Also, the cantilevered cleats are not only relatively unprotected from damage, but also would act like the teeth of a saw to abraid against any object on the side thereof. Another disadvantage of the referenced shoe is the decreased stiffness or lateral beam strength of the shoe due to the discontinuous nature of the cleats when taken in conjunction with the longitudinal section of the irregular cast frame.